Reversible coordination of N(2) and H(2) to a homoleptic S = 1/2 Fe(i) diphosphine complex in solution and the solid state

The synthesis and characterisation of the S = 1/2 Fe(i) complex [Fe(depe)(2)](+)[BArF4](–) ([1](+)[BArF4](–)), and the facile reversible binding of N(2) and H(2) in both solution and the solid state to form the adducts [1·N(2)](+) and [1·H(2)](+), are reported. Coordination of N(2) in THF is thermodynamically favourable under ambient conditions (1 atm; ΔG(298) = –4.9(1) kcal mol(–1)), while heterogenous binding is more favourable for H(2) than N(2) by a factor of ∼300. [1·H(2)](+)[BArF4](–) represents a rare example of a well-defined, open-shell, non-classical dihydrogen complex, as corroborated by ESR spectroscopy. The rapid exchange between N(2) and H(2) coordination under ambient conditions is unique for a paramagnetic Fe complex.